Solar cell and method for manufacturing the same

ABSTRACT

A solar cell according to an embodiment includes a semiconductor substrate; a first dopant layer formed at one surface of the semiconductor substrate; and a first electrode electrically connected to the first dopant layer. At least a part of the first dopant layer includes a pre-amorphization element, and a concentration of the pre-amorphization element in one portion of the first dopant layer is different from a concentration of the pre-amorphization element in another portion of the first dopant layer.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to and the benefit of Korean PatentApplication No. 10-2012-0050315, filed on May 11, 2012 in the KoreanIntellectual Property Office, the disclosure of which is incorporatedherein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The embodiments of the invention relate to a solar cell and a method formanufacturing the same, and more particularly, to a solar cell includinga dopant layer and a method for manufacturing the same.

2. Description of the Related Art

Recently, as existing energy resources such as oil or coal are expectedto be exhausted, an interest in alternative energy resources forreplacing oil or coal is increasing. In particular, a solar cell thatdirectly converts or transforms solar energy into electricity using asemiconductor member is gaining attention.

In a solar cell, a p-n junction is formed by forming a dopant layer inorder to induce photoelectric conversion, and an electrode electricallyconnected to the dopant layer of an n-type or a p-type is formed.However, a doping profile of the dopant layer is not easily controlled,and properties of the dopant layer deteriorate, thereby reducingefficiency of the solar cell.

SUMMARY OF THE INVENTION

The embodiments of the invention are directed to provide a solar cellhaving enhanced efficiency due to a controlled doping profile and amethod for manufacturing the solar cell.

A solar cell according to an embodiment of the invention includes asemiconductor substrate; a first dopant layer formed at one surface ofthe semiconductor substrate; and a first electrode electricallyconnected to the first dopant layer. At least a part of the first dopantlayer includes a pre-amorphization element, and a concentration of thepre-amorphization element in one portion of the first dopant layer isdifferent from a concentration of the pre-amorphization element inanother portion of the first dopant layer.

A method for manufacturing a solar cell according to an embodiment ofthe invention includes preparing a semiconductor substrate;ion-implanting a pre-amorphization element to form an amorphous layer atleast apart of one surface of the semiconductor substrate;ion-implanting a first conductive type dopant to the one surface of thesemiconductor substrate to form a first dopant layer; and forming afirst electrode electrically connected to the first dopant layer. Aconcentration of the pre-amorphization element in one portion of thefirst dopant layer is different a concentration of the pre-amorphizationelement in another portion of the first dopant layer.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of a solar cell according to anembodiment of the invention.

FIG. 2 is a schematic plan view of an emitter layer and a firstelectrode of the solar cell shown in FIG. 1.

FIG. 3 is a block diagram for illustrating a method for manufacturing asolar cell according to an embodiment of the invention.

FIGS. 4a to 4g are cross-sectional views for illustrating the method formanufacturing the solar cell according to the embodiment of theinvention.

FIG. 5 is a cross-sectional view of a solar cell according to anotherembodiment of the invention.

FIG. 6 is a cross-sectional view of a solar cell according to yetanother embodiment of the invention.

FIG. 7 is a cross-sectional view of a solar cell according to stillanother embodiment of the invention.

FIG. 8 is a graph of relative values of sheet resistances of a secondportion of an emitter where argon is ion-implanted in each ofExperimental Embodiments and Comparative Examples.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Hereinafter, embodiments of the invention will be described withreference to the accompanying drawings. However, the embodiments of theinvention are not limited the embodiments, and the various modificationsof the embodiments are possible.

In order to clearly and concisely illustrate the embodiments of theinvention, members not related to the embodiments of the invention areomitted in the figures. Also, members similar to or the same as eachother have the same reference numerals in the figures. In addition,dimensions of layers and regions are exaggerated or schematicallyillustrated, or some layers are omitted for clarity of illustration. Inaddition, the dimension of each part as drawn may not reflect an actualsize.

In the following description, when a layer or substrate “includes”another layer or portion, it can be understood that the layer orsubstrate can further include still another layer or portion. Also, whena layer or film is referred to as being “on” another layer or substrate,it can be understood that the layer of film is directly on the otherlayer or substrate, or intervening layers may also be present. Further,when a layer or film is referred to as being “directly on” another layeror substrate, it can be understood that the layer or film is directly onthe another layer or substrate, and thus, there is no intervening layer.

Hereinafter, a solar cell and a method for manufacturing the sameaccording to embodiments of the invention will be described withreference to the accompanying drawings.

FIG. 1 is a cross-sectional view of a solar cell according to anembodiment of the invention, and FIG. 2 is a schematic plan view of anemitter layer and a first electrode of the solar cell shown in FIG. 1.

Referring to FIGS. 1 and 2, a solar cell 100 according to an embodimentincludes a semiconductor substrate 10, dopant layers 20 and 30 formed atthe semiconductor substrate 10, and electrodes 24 and 34 electricallyconnected to the semiconductor substrate 10 or the dopant layers 20 and30. More specifically, the dopant layers 20 and 30 may include a firstdopant layer (hereinafter, referred to as “an emitter layer”) 20 formedat or adjacent to a first surface (hereinafter, referred to as “a frontsurface”) of the semiconductor substrate 10, and a second dopant layer(hereinafter, referred to as “a back surface field layer”) 30 formed ator adjacent to a second surface (hereinafter, referred to as “a backsurface”) of the semiconductor substrate 10. Also, the electrodes 24 and34 may include a first electrode (or a plurality of first electrodes) 24electrically connected to the emitter layer 20, and a second electrode(or a plurality of second electrodes) 34 electrically connected to thesemiconductor substrate 10 or the back surface field layer 30. Inaddition, the solar cell 100 may further include an anti-reflectionlayer 22 and a passivation layer 32. This will be described in moredetail.

The semiconductor substrate 10 may include one or more of varioussemiconductor materials. For example, the semiconductor substrate 10 mayinclude silicon having a dopant of a second conductivity type. Singlecrystal silicon or polycrystalline silicon may be used for the silicon,and the second conductivity type may be an n-type. That is, thesemiconductor substrate 10 may include single crystal silicon orpolycrystalline silicon having a group V element, such as phosphorus(P), arsenic (As), bismuth (Bi), antimony (Sb), or the like.

When the semiconductor substrate 10 has the n-type dopant as in theabove, the emitter layer 20 of a p-type is formed at the front surfaceof the semiconductor substrate 10, and thereby forming a p-n junction.When light, such as sun light, is incident to the p-n junction,electron-hole pairs are generated, and the electrons generated by thephotoelectric effect moves to the back surface of the semiconductorsubstrate 10 and are collected by the second electrode 34, and the holesgenerated by the photoelectric effect moves to the front surface of thesemiconductor substrate 10 and are collected by the first electrode 24.Then, electric energy is generated thereby.

In this instance, the holes having mobility lower than that of theelectrodes move to the front surface of the semiconductor substrate 10,not the back surface of the semiconductor substrate 10. Therefore, theconversion efficiency of the solar cell 100 can be enhanced.

The front and/or back surfaces of the semiconductor substrate 10 may bea textured surface to have protruded and/or depressed portions ofvarious shapes (such as a pyramid shape). Thus, surface roughness isincreased by the protruded and/or depressed portions, and reflectance ofthe incident sun light at the front surface of the semiconductorsubstrate 10 can be reduced by the texturing. Then, an amount of thelight reaching the p-n junction between the semiconductor substrate 10and the emitter layer 20 can increase, thereby reducing an optical lossof the solar cell 100.

However, the embodiments of the invention are not limited thereto, andthus, the protruded and/or depressed portions may be formed at only onesurface (especially, the front surface), or there may be no protrudedand/or depressed portions at the front and back surfaces.

The emitter layer 20 including a first conductive type dopant 204 may beformed at the front surface of the semiconductor substrate 10. A p-typedopant such as a group III element (for example, boron (B), aluminum(Al), gallium (Ga), indium (In) or the like) may be used for the firstconductive type dopant 204. In the embodiment of the invention, theemitter layer 20 includes a pre-amorphization element 202 partially (orlocally), as well as the first conductive type dopant 204.

In the embodiment of the invention, the emitter layer 20 includes afirst portion 20 a, and a second portion 20 b other than the firstportion 20 a. The first portion 20 a is adjacent to the first electrode24 and is in contact with the first electrode 24. Referring to FIG. 2,the first portion 20 a is formed at a portion overlapping the firstelectrode 24. The second portion 20 b including the pre-amorphizationelement 202 (refer to FIG. 1) is formed at the other portion and isapart from the first electrode 24.

The first portion 20 a has a relatively high doping concentration andhas a relatively low resistance, and the second portion 20 b has arelatively low doping concentration and has a relatively highresistance. That is, in the embodiment of the invention, the shallowemitter can be achieved by forming the second portion 20 b having therelatively high resistance at a portion where the sun light is incidentbetween adjacent first electrodes 24, and thereby enhancing the currentdensity of the solar cell 100. In addition, contact resistance with thefirst electrode 24 can be reduced by forming the first portion 20 ahaving the relatively low resistance at a portion that is in contactwith the first electrode 24. That is, when the emitter layer 20 has theselective emitter structure, the efficiency of the solar cell 100 can beincreased or maximized.

When the first portion 20 a is thin, the first electrode 24 maypenetrate the first portion 20 a and be in contact with thesemiconductor substrate 10 where the emitter layer 20 is not formed,thereby inducing a shunt. Thus, in the embodiment of the invention, thefirst portion 20 a may be thicker than the second portion 20 b. That is,a junction depth of the first portion 20 a may be deeper than that ofthe second portion 20 b.

In this instance, in the embodiment of the invention, only apart of theemitter layer 20 (that is, the second portion 20 b having the relativelyhigh resistance) includes the pre-amorphization element 202, and thefirst portion 20 a does not include the pre-amorphization element 202.That is, the first portion 20 a includes the first conductive typedopant 204 only, and the second portion 20 b includes both the firstconductive type dopant 204 and the pre-amorphization element 202.

The pre-amorphization element 202 is an element for forming an amorphouslayer at the semiconductor substrate 10 before doping the firstconductive type dopant 204 to the semiconductor substrate 10. Thepre-amorphization element may have similar properties with thesemiconductor substrate 10 or may be inert elements not reacting withthe semiconductor substrate 10, so that the pre-amorphization elementsdo not affect the properties (e.g., electrical properties) of thesemiconductor substrate 10. Thus, the pre-amorphization element 202 maybe argon, silicon, germanium, fluorine, and so on.

The pre-amorphization element 202 may have an atomic number the same asor larger than that of the first conductive type dopant 204, and massand size of the pre-amorphization element 202 may be the same as orlarger than the first conductive type dopant 204. However, by increasinga dose and an ion-implantation energy of the pre-amorphization element202 during an ion-implantation, an element (such as the fluorine) beingsmaller than or having an atomic number smaller than the firstconductive type dopant 204 or the element constituting semiconductorsubstrate 10 may be used for the pre-amorphization element 202.

Since the pre-amorphization element 202 is included only in the secondportion 20 b, a projected range (Rp) of the first conductive type dopant204 in the second portion 20 b can be controlled. On the other hand,conventionally, when a light ion such as boron is used for the firstconductive type dopant 204, the ion can be implanted deeper than ageneral projected range (or an ion-implantation depth) by a channelingeffect. Therefore, controlling the projected range is difficult. Thisproblem is more seriously generated at the second portion 20 b than thefirst portion 20 a that is in contact with the first electrode 24 and isa relatively thick. Accordingly, in the embodiment of the invention,after a pre-amorphization of a portion corresponding to the secondportion 20 b of the semiconductor substrate 10, the first conductivetype dopant 204 is ion-implanted. Thus, the projected range of the firstconductive type dopant 204 can be controlled at the second portion 20 b.For this reason, sheet resistance of the second portion 20 b canincrease. This will be described later in more detail when a method formanufacturing the solar cell 100 is described.

In the embodiment of the invention, the second portion 20 b is thin (orrelatively thinner), and thus, is effectively recovered during aheat-treatment for activation performed after the ion-implantation.Likewise, in the embodiment of the invention, the efficiency of thesolar cell 100 can be enhanced by optimizing a doping profile of theemitter layer 20. Also, the pre-amorphization element 202 acts as aBettering element, and thus, property of the solar cell 100 can beenhanced even more.

In the second portion 20 b, a concentration of the pre-amorphizationelement 202 may be higher than a concentration of the first conductivetype dopant 204. Then, by sufficiently forming the amorphous layer atthe portion corresponding to the second portion 20 b, the projectedrange of the first conductive type dopant 204 at the second portion 20 bcan be effectively controlled.

For example, in the second portion 20 b, the concentration of thepre-amorphization element 202 is about 3 to 20 times the concentrationof the first conductive type dopant 204. This is caused by a differencein dose. When a concentration ratio is less than 3 times, the portioncorresponding to the second portion 20 b may become not sufficientlyamorphous and the controlling of the projected range of the firstconductive type dopant 204 may be difficult. When the concentrationratio is more than 20 times, the concentration of the pre-amorphizationelement 202 may be too high and the emitter layer 20 may bedeteriorated. For considering a sufficient amorphization and a greaterenhancement of the property of the emitter layer 20, the concentrationratio may be about 5 to 15 times.

As in the above, a thickness of the second portion 20 b can becontrolled by the pre-amorphization element 202. For example, the firstportion 20 a may have a thickness of about 0.8 to 2.0 μm, and the secondportion 20 b may have a thickness of about 0.1 to 0.6 μm. However, theembodiments of the invention are not limited thereto. The thicknesses ofthe first and second portions 20 a and 20 b may be varied.

The anti-reflection layer 22 and the first electrode 24 may be formed onthe emitter 20 at the front surface of the semiconductor substrate 10.

The anti-reflection layer 22 may be formed substantially at the entirefront surface of the semiconductor substrate 10, except for the portionwhere the first electrode 24 is formed. The anti-reflection layer 22reduces reflectance (or reflectivity) of sun light incident to the frontsurface of the semiconductor substrate 10. By reducing the reflectanceof sun light incident to the front surface of the semiconductorsubstrate 10, an amount of the sun light reaching the p-n junctionformed between the semiconductor substrate 10 and the emitter layer 20can be increased, thereby increasing a short circuit current (Isc) ofthe solar cell 100.

Also, the anti-reflection layer 22 passivates defects at a surface or abulk of the emitter layer 20. By passivating the defects at the emitterlayer 20, recombination sites of minority carrier are reduced oreliminated, thereby increasing an open-circuit voltage (Voc) of thesolar cell 100. Accordingly, the open-circuit voltage and theshort-circuit current of the solar cell 100 can be increased by theanti-reflection layer 22, and thus, the efficiency of the solar cell 100can be enhanced.

The anti-reflection layer 22 may include one or more of variousmaterials. For example, the anti-reflection layer 22 may include asilicon nitride layer. However, the embodiments of the invention are notlimited thereto. Thus, the anti-reflection layer 22 may have a singlefilm structure or a multi-layer film structure including, for example,at least one material selected from a group consisting of siliconnitride, silicon nitride including hydrogen, silicon oxide, silicon oxynitride, MgF₂, ZnS, TiO₂ and CeO₂.

The first electrode 24 is electrically connected to the emitter layer 20by penetrating the anti-reflection layer 22 at the front surface of thesemiconductor substrate 10. The first electrode 24 may have variousshapes in a plan view. For example, as shown in FIG. 2, the firstelectrode 24 may include a plurality of finger electrodes 24 a. Thefinger electrodes 24 a are parallel to each other and are spaced apartfrom each other with a first distance D1. Also, the first electrode 24may include a bus electrode 24 b being extended in a direction crossingthe finger electrodes 24 a to connect the finger electrodes 24 a. Thebus electrode 24 b may include a single bus electrode 24 b, or the buselectrode 24 b may include a plurality of bus electrodes 24 b as shownin FIG. 2. The plurality of bus electrodes 24 b are spaced apart fromeach other with a second distance D2 larger than the first distance D1.Also, the finger electrode 24 a may have a width W1 smaller than a widthW2 of the bus bar electrode 24 b. However, the embodiments of theinvention are not limited thereto. Thus, the finger electrode 24 a mayhave the width W1 same as the width W2 of the bus bar electrode 24 b.That is, the shape of the first electrode 24 is just an example, and theembodiments of the invention are not limited thereto. Also, the firstelectrode 24 may include one or more or various materials. Examples ofsuch materials may include silver (Ag), or other metals.

Referring to FIG. 1 again, the back surface field layer including thesecond conductive type dopant with a high concentration is formed at theback surface of the semiconductor substrate 10. An n-type dopant such asa group V element (such as phosphorus (P), arsenic (As), bismuth (Bi),antimony (Sb), or the like) may be used as the second conductive typedopant 304. In the embodiment of the invention, the back surface fieldlayer 30 may include a pre-amorphization element 302 partially (orlocally), as well as the second conductive type dopant 304. This will bedescribed in more detail.

In the embodiment of the invention, the back surface field layer 30includes a first portion 30 a, and a second portion 30 b other than thefirst portion 30 a. The first portion 30 a is adjacent to the secondelectrode 34 and is in contact with the second electrode 34. Thestructures of the shape of the back surface field layer 30 and thesecond electrode 34 in a plan view are similar to the structure of theshape of the emitter layer 20 and the first electrode 24 in a plan viewshown in FIG. 2. Thus, a detailed description is omitted.

The first portion 30 a has a relatively high doping concentration andhas a relatively low resistance, and the second portion 30 b has arelatively low doping concentration and has a relatively highresistance. That is, in the embodiment of the invention, therecombination of the electrons and holes can be reduced or prevented byforming the second portion 30 b having the relatively high resistance ata portion between the adjacent second electrodes 34, and therebyenhancing the current density of the solar cell 100. In addition,contact resistance with the second electrode 34 can be reduced byforming the first portion 30 a having the relatively low resistance at aportion that is in contact with the second electrode 34. That is, whenthe back surface field layer 30 has the selective back surface fieldstructure, the efficiency of the solar cell 100 can be increased ormaximized.

Also, as the first portion 20 a is thicker than the second portion 20 bat the emitter layer 20, the first portion 30 a also may be thicker thanthe second portion 30 b at the back surface field layer 30.

In this instance, in the embodiment of the invention, only a part of theback surface field layer 30 (that is, the second portion 30 b having therelatively high resistance) includes the pre-amorphization element 302,and the first portion 30 a does not include the pre-amorphizationelement 302. That is, the first portion 30 a includes the secondconductive type dopant 304 only, and the second portion 30 b includesboth the second conductive type dopant 304 and the pre-amorphizationelement 302. The pre-amorphization element 302 is similar to thepre-amorphization element 202, and thus, a detailed description isomitted.

The pre-amorphization element 302 may have an atomic number the same asor larger than that of the second conductive type dopant 304, and massand size of the pre-amorphization element 302 may be the same as orlarger than the second conductive type dopant 304. However, byincreasing a dose and an ion-implantation energy of thepre-amorphization element 302 during the ion-implantation, an element(such as the fluorine) being smaller than or having an atomic numbersmaller than the second conductive type dopant 304 or the elementconstituting semiconductor substrate 10 may be used for thepre-amorphization element 302.

Since the pre-amorphization element 302 is included only in the secondportion 30 b, a projected range of the second conductive type dopant 304at the second portion 30 b can be controlled. Also, sheet resistance ofthe second portion 30 b can increase. Likewise, in the embodiment of theinvention, the efficiency of the solar cell 100 can be enhanced byoptimizing a doping profile of the back surface field layer 30.

In the second portion 30 b, a concentration of the pre-amorphizationelement 302 may be higher than a concentration of the second conductivetype dopant 304. Then, by sufficiently forming the amorphous layer atthe portion corresponding to the second portion 30 b, the projectedrange of the second conductive type dopant 304 at the second portion 30b can be effectively controlled.

For example, in the second portion 30 b, the concentration of thepre-amorphization element 302 is about 3 to 20 times the concentrationof the second conductive type dopant 304. This is caused by a differencein dose. When a concentration ratio is less than 3 times, the portioncorresponding to the second portion 30 b may become insufficientlyamorphous and the controlling of the projected range of the secondconductive type dopant 304 may be difficult. When the concentrationratio is more than 20 times, the concentration of the pre-amorphizationelement 302 may be too high and the back surface field layer 30 may bedeteriorated. For considering a sufficient amorphization and a greaterenhancement of the property of the back surface field layer 30, theconcentration ratio may be about 5 to 15 times.

The passivation layer 32 and the second electrode 34 may be formed atthe back surface of the semiconductor substrate 10.

The passivation layer 32 may be formed substantially at the entire backsurface of the semiconductor substrate 10, except for the portions wherethe second electrode 34 is formed. The passivation layer 32 passivatesdefects at the back surface of the semiconductor substrate 10, andeliminates the recombination sites of minority carrier. Thus, an opencircuit voltage of the solar cell 100 can be increased.

The passivation layer 32 may include a transparent insulating materialfor passing the light. Thus, the light can be incident to the backsurface of the semiconductor substrate 10 through the passivation layer32, and thereby enhancing the efficiency of the solar cell 100. Thepassivation layer 32 may have a single film structure or a multi-layerfilm structure including, for example, at least one material selectedfrom a group consisting of silicon nitride, silicon nitride includinghydrogen, silicon oxide, silicon oxy nitride, MgF₂, ZnS, TiO₂ and CeO₂.However, the embodiments of the invention are not limited thereto, andthus, the passivation film 32 may include one or more of variousmaterials.

The second electrode 34 may include a metal having a high electricconductivity. The structure of the second electrode 34 is similar to thestructure of the first electrode 24 shown in FIG. 2, and detaileddescriptions thereof are omitted.

In the embodiment of the invention, the emitter layer 20 and the backsurface field layer 30, which are the dopant layers, include thepre-amorphization element 202 and 302 partially (or locally). Therefore,the thicknesses of the second portions 20 b and 30 b not in contact withthe electrode 24 and 34 can be controlled and the properties of thesecond portions 20 b and 30 b can be enhanced. Accordingly, theefficiency of the solar cell 100 can be enhanced.

Hereinafter, a method for forming a solar cell according to anembodiment of the invention will be described in more detail withreference to FIG. 3, and FIGS. 4a to 4g . In the following description,any described portions already described above will be omitted, and anyportions not already described above will be described in detail.

FIG. 3 is a block diagram for illustrating a method for manufacturing asolar cell according to an embodiment of the invention. FIGS. 4a to 4gare cross-sectional views for illustrating the method for manufacturingthe solar cell according to the embodiment of the invention.

Referring to FIG. 3, a method for manufacturing a solar cell accordingto the embodiment includes an operation ST10 for preparing asemiconductor substrate, an operation ST20 for ion-implanting apre-amorphization element, an operation ST30 for ion-implanting a firstconductive type dopant, an operation ST40 for ion-implanting a secondconductive type dopant, an operation ST50 for heat-treating foractivation, an operation ST60 for forming an anti-reflection film and apassivation film, and an operation ST70 for forming an electrode.

First, as shown in FIG. 4a , in the operation ST10 for preparing thesemiconductor substrate, a semiconductor substrate 10 having a secondconductive type dopant is prepared. The front and back surfaces of thesilicon semiconductor substrate 10 may be textured to have protrudedand/or dented portions of various shapes (or to have an uneven surface).For the texturing method, a wet etching method or a dry etching methodmay be used. In the wet etching method, the substrate 10 may be dippedinto a texturing solution. According to the wet etching method, theprocess time can be short. In the dry etching method, the surface of thesemiconductor substrate 10 is etched by a diamond drill or a laser. Inthe dry etching method, the protruded and/or dented portions can beuniformly formed, though the semiconductor substrate 10 may be damagedand the process time may be long. Accordingly, the semiconductorsubstrate 10 may be textured by one or more of various methods.

Next, as shown in FIG. 4b , in step ST20 for ion-implanting apre-amorphization element, the pre-amorphization element 202 ision-implanted into the front surface of the semiconductor substrate 10partially (or locally), and the pre-amorphization element 302 ision-implanted into the back surface of the semiconductor substrate 10partially (or locally). More specifically, the pre-amorphizationelements 202 and 302 are ion-implanted to portions corresponding tosecond portions 20 b and 30 b (refer to FIG. 1) of dopant layers (referto FIG. 1). In this instance, masks 206 and 306 having opening portionsformed at the portion corresponding to second portions 20 b and 30 b mayused so that the pre-amorphization elements 202 and 302 areion-implanted partially (or locally). However, the present invention isnot limited thereto.

Accordingly, a first amorphous portion 202 a is formed at a portioncorresponding to the second portion 20 b of an emitter layer (refer toFIG. 1) at the front surface of the semiconductor substrate 10, and asecond amorphous portion 302 a is formed at a portion corresponding tothe second portion 30 b of an back surface field layer 30 (refer toFIG. 1) at the back surface of the semiconductor substrate 10.

In this instance, the dose of the pre-amorphization element 202 or 302may be in a range of about 1×10¹⁴ to 9×10¹⁶ atoms/cm². This dose rangeis determined to sufficiently form the first or second amorphous portion202 a or 302 a at the semiconductor substrate 10. The dose of thepre-amorphization element 202 and 302 may be larger than the dose of afirst or second conductive type dopant 204 or 304 (that will beion-implanted in the operations 30 and 40), respectively. This is forreducing or preventing the first and second conductive type dopants 204and 304 from being deeply implanted by sufficiently forming the firstand second amorphous portions 202 a and 302 a. As described above, thedoses of the pre-amorphization elements 202 and 302 may be about 3 to 20times the doses of the first and second conductive type dopants 204 and304, respectively.

The ion-implantation energy of each of the pre-amorphization elements202 and 302 may be in a range of about 0.1 to 100 keV. Thision-implantation energy range is determined to sufficiently form thefirst or second amorphous portion 202 a or 302 a at the semiconductorsubstrate 10. The ion-implantation energy of the pre-amorphizationelements 202 and 302 may be larger than the ion-implantation energy of afirst or second conductive type dopant 204 or 304 (that will beion-implanted in the operations 30 and 40), respectively. This is forreducing or preventing the first and second conductive type dopant 204and 304 from being deeply implanted by sufficiently forming the firstand second amorphous portions 202 a and 302 a.

In the embodiment of the invention, after ion-implanting thepre-amorphization element 202 to the front surface of the semiconductorsubstrate 10, the pre-amorphization element 302 may be ion-implanted tothe back surface of the semiconductor substrate 10. Selectively (oralternatively), after ion-implanting the pre-amorphization element 302to the back surface of the semiconductor substrate 10, thepre-amorphization element 202 may be ion-implanted to the front surfaceof the semiconductor substrate 10.

Next, as shown in FIG. 4c , in the operation ST30 for ion-implanting afirst conductive type dopant, a first conductive type dopant 204 such asboron or gallium is ion-implanted to the entire front surface of thesemiconductor substrate 10.

In this instance, the first conductive type dopant 204 may beion-implanted to the front surface of the semiconductor substrate 10with a uniform dose. Selectively (or alternatively), the dose of thefirst conductive type dopant 204 at the first portion 20 a may largerthan the dose of the first conductive type dopant 204 at the secondportion 20 b. When there is a dose difference between the first portion20 a and the second portion 20 b, a comb mask may be used. However, theembodiments of the invention are not limited thereto. Thus, the numberof the ion-implantation process may be different at the first and secondportions 20 a and 20 b. Other methods may be used.

When the first conductive type dopant 204 is ion-implanted to the entirefront surface of the semiconductor substrate 10, at the first amorphousportion 202 a corresponding to the second portion 20 b, the firstconductive type dopant 204 is implanted only to the first amorphousportion 202 a. Accordingly, the projected range of the second portion 20b can be controlled. On the other hand, at the portion corresponding tothe first portion 20 a, the first amorphous portion 202 a is not formedand the first conductive type dopant 204 is deeply implanted more thanthe first amorphous portion 202 a.

In this instance, the dose of the first conductive type dopant 204 maybe in a range of about 1×10¹⁴ to 9×10¹⁵ atoms/cm², and theion-implantation energy thereof may be in a range of about 0.1 to 30keV. This is determined so that the emitter layer 20 can have a suitableresistance based on the concentration of the first conductive typedopant 204, and so that the damage of the semiconductor substrate 10 canbe reduced or prevented.

Next, as shown in FIG. 4d , in the operation ST40 for ion-implanting asecond conductive type dopant, a second conductive type dopant 304 suchas phosphorus is ion-implanted to the entire back surface of thesemiconductor substrate 10.

In this instance, the second conductive type dopant 304 may beion-implanted to the back surface of the semiconductor substrate 10 witha uniform dose. Selectively (or alternatively), the dose of the secondconductive type dopant 304 at a first portion 30 a may larger than thedose of the second conductive type dopant 304 at a second portion 30 b.When there is a dose difference between the first portion 30 a and thesecond portion 30 b, a comb mask may be used. However, the embodimentsof the invention are not limited thereto. Thus, the number of theion-implantation process may be different at the first and secondportions 30 a and 30 b. Other methods may be used.

When the second conductive type dopant 304 is ion-implanted to theentire back surface of the semiconductor substrate 10, at the secondamorphous portion 302 a corresponding to the second portion 30 b, thesecond conductive type dopant 304 is implanted only to the secondamorphous portion 302 a. Accordingly, the projected range of the secondportion 30 b can be controlled. On the other hand, at the portioncorresponding to the first portion 30 a, the second amorphous portion302 a is not formed and the second conductive type dopant 304 is deeplyimplanted more than the second amorphous portion 302 a.

In this instance, the dose of the second conductive type dopant 304 maybe in a range of about 1×10¹⁴ to 9×10¹⁵ atoms/cm², and theion-implantation energy thereof may be in a range of about 0.1 to 30keV. This is determined so that the back surface field layer 30 can havea suitable resistance based on the concentration of the secondconductive type dopant 304, and so that the damage of the semiconductorsubstrate 10 can be reduced or prevented.

In the embodiment of the invention, after ion-implanting the firstconductive type dopant 204, the second conductive type dopant 304 ision-implanted. However, the present invention is not limited thereto.Therefore, after ion-implanting the second conductive type dopant 304,the first conductive type dopant 204 may be implanted.

Also, in the embodiment of the invention, before ion-implanting of thefirst conductive type dopant 204 and the second conductive type dopant304, both of the pre-amorphization elements 202 and 302 areion-implanted. However, the present invention is not limited thereto.Therefore, the ion-implantation sequence may be varied if the condition(that is, the pre-amorphization element 202 is ion-implanted before thefirst conductive type dopant 204 is ion-implanted, and thepre-amorphization element 302 is ion-implanted before the secondconductive type dopant 304 is ion-implanted) is satisfied.

Next, as shown in FIG. 4e , in the operation ST50 for heat-treating foractivation, the first conductive type dopant 204 and the secondconductive type dopant 304 ion-implanted to the semiconductor substrate10 are activated by heat. Accordingly, an emitter layer 20 including thefirst and second portion 20 a and 20 b are formed at the front surfaceof the semiconductor substrate 10, and a back surface field layer 30including the first and second portion 30 a and 30 b are formed at theback surface of the semiconductor substrate 10.

In this instance, because the portions corresponding to the secondportions 20 b and 30 b of the semiconductor substrate 10 are amorphousby the pre-amorphization elements 202 and 302, growth through solidphase epitaxy is induced. Accordingly, the second portions 20 b and 30 bcan be easily recovered, and the sheet resistance of the second portions20 b and 30 b can increase. Also, the first and second conductive typedopants at the first portions 20 a and 30 a are diffused deeply into aninside of the semiconductor substrate 10, and the first portions 20 aand 30 a become thicker.

When the first conductive type dopant 204 and the second conductive typedopant 304 are co-activated, the temperature of the heat-treating may beabout 900 to 1200° C. When the temperature is higher than about 1200°C., problems due to the high temperature may be generated. When thetemperature is lower than about 900° C., the activation and the solidstate epitaxy may be not induced sufficiently. By the co-activation, theprocess can be simple and the productivity can be increased.

However, the embodiments of the invention are not limited thereto. Thus,the first conductive type dopant 204 may be ion-implanted, and then, thefirst conductive type dopant 204 may be heat-treated for the activation.After that, the second conductive type dopant 304 may be ion-implanted,and then, the second conductive type dopant 304 may be heat-treated forthe activation. When the activation of the first conductive type dopant204 and the activation of the second conductive type dopant 304 areseparately performed, the heat-treating can be performed at thetemperature suitable for the activation of each dopant.

Next, as shown in FIG. 4f , in the operation ST60 for forming theanti-reflection film and the passivation film, an anti-reflection film22 and a passivation film 32 are formed on the front surface and theback surface of the semiconductor substrate 10, respectively. Theanti-reflection film 22 and the passivation film 32 may be formed by oneor more of various methods such as vacuum evaporation, chemical vapordeposition, spin coating, screen printing, or spray coating.

Next, as shown in FIG. 4g , in the operation ST70 for forming theelectrode, a first electrode 24 electrically connected to the emitterlayer 20 is formed at the front surface of the semiconductor substrate10 and a second electrode 34 electrically connected to the back surfacefield layer 30 is formed at the back surface of the semiconductorsubstrate 10.

After forming an opening at the anti-reflection layer 22, the firstelectrode 24 may be formed inside the opening by one or more of variousmethods, such as a plating method or a deposition method. Also, afterforming an opening at the second passivation layer 32, the secondelectrode 34 may be formed inside the opening by one or more of variousmethods, such as a plating method or a deposition method.

Selectively (or alternatively), the first and second electrodes 24 and34 may be formed by fire-through or laser firing contact of printedpastes for the first and second electrodes 24 and 34. For example, thepastes may be printed by various methods such as a screen printingmethod. In this instance, because the openings are naturally (orautomatically) formed during the fire-through or the laser firingcontact, separate operations for forming the openings and are notnecessary.

In the embodiment of the invention, before ion-implanting the first andsecond conductive type dopants 204 and 304, the pre-amorphizationelements 202 and 302 are partially (or locally) ion-implanted (morespecifically, the pre-amorphization elements 202 and 302 areion-implanted to the second portions 20 b and 30 b that are not incontact with the electrode 24 and 34). Accordingly, the first and secondamorphous portions 202 a and 302 a are formed to correspond to thesecond portions 20 b and 30 b, respectively. Then, when the first andsecond conductive type dopants 204 and 304 are ion-implanted, at thefirst and second amorphous portions 202 a and 302 a, the first andsecond conductive type dopants 204 and 304 are implanted only to thefirst and second amorphous portions 202 a and 302 a. Thus, the projectedrange can be controlled. Accordingly, the second portions 20 b and 30 bduring the heat-treating for the activation can be easily recovered, andthe sheet resistance of the second portions 20 b and 30 b can increase.Accordingly, the properties of the emitter layer 20 and the back surfacefield layer 30 can be enhanced, thereby enhancing the solar cell 100.

In the above embodiment of the invention, both of the emitter layer 20and the back surface field layer 30 include the pre-amorphizationelement 202 or 302. However, the embodiments of the invention are notlimited thereto. Thus, one of the emitter layer and the back surfacefield layer 30 may include the pre-amorphization element 202 or 302.Also, as shown in FIG. 5, the back surface field layer 30 does notinclude the pre-amorphization element 302 and includes the secondconductive type dopant 304, and the concentration of the secondconductive type dopant 304 may be entirely uniform. Selectively (oralternatively), as shown in FIG. 6, the emitter layer 20 does notinclude the pre-amorphization element 202 and includes the firstconductive type dopant 204, and the concentration of the firstconductive type dopant 204 may be entirely uniform.

Selectively (or alternatively), one of the dopant layers 20 and 30 mayinclude the pre-amorphization element 202 and 302 partially (orlocally), and the other one of the dopant layers 20 and 30 may includethe pre-amorphization element 202 or 302 entirely.

In addition, in the above embodiment of the invention, the secondportions 20 b and 30 b of the emitter layer 20 and the back surfacefield layer 30 include the pre-amorphization elements 202 and 302,respectively, and the first portions 20 a and 30 a do not include thepre-amorphization elements 202 and 302. However, in the operation ST20for ion-implanting the pre-amorphization element, although the masks 206and 306 (refer to FIG. 4b ) are used, the pre-amorphization elements 202and 302 may be implanted to the first portions 20 a and 30 a. In thisinstance, the concentration of the pre-amorphization element 202 and 302in the second portions 20 b and 30 b are higher than the concentrationof the pre-amorphization element 202 and 302 in the first portions 20 aand 30 a, respectively.

That is, as shown in FIG. 7, the first portions 20 a and 30 a as well asthe second portions 20 b and 30 b may include the pre-amorphizationelements 202 and 302. That is, as shown in a portion of an inside of adotted line in an enlarged portion of FIG. 7, areas of the firstportions 20 a and 30 a that are adjacent to the second portions 20 b and30 b, respectively, may include the pre-amorphization elements 202 and302. In areas that approach the second portions 20 b and 30 b, thedoping amount and the projected range (ion-implantation depth) maybecome deeper. Although the masks 206 and 306 are used, this phenomenonof inclusion of the pre-amorphization elements 202 and 302 in portionsof the first portions 20 a and 30 a may be induced by a process error.In FIG. 7 and the related descriptions, a part of the first portions 20a and 30 a include the pre-amorphization elements 202 and 302,respectively. However, the embodiments of the invention are not limitedthereto. Thus, entire portions of the first portions 20 a and 30 a mayinclude the pre-amorphization elements 202 and 302 of a lowconcentration.

In the above embodiment of the invention, the semiconductor substrate 10and the back surface field layer 30 are the n-types, and the emitterlayer 20 is the p-type. However, the embodiments of the invention arenot limited thereto. The semiconductor substrate 10 and the back surfacefield layer 30 may be the p-types, and the emitter layer 20 may be then-type.

Hereinafter, the embodiments of the invention will be described in moredetail through experimental examples. The experimental examples areprovided only for illustrative purpose of the embodiments of theinvention and the embodiments of the invention are not limited thereto.

Experimental Embodiments

An n-type semiconductor substrate was prepared. Argon was ion-implantedto a front surface and a back surface of the semiconductor substrate.Then, boron as a p-type dopant was ion-implanted to the front surface ofthe semiconductor substrate, and phosphorus as an n-type dopant wasion-implanted to the back surface of the semiconductor substrate. Aheat-treating for activation was performed at a temperature of 1000° C.,and an emitter layer and a back surface field layer were formed.

An anti-reflection film was formed on the front surface of thesemiconductor substrate, and a passivation film was formed on the backsurface of the semiconductor substrate. Then, a first electrodeelectrically connected to the emitter layer and a second electrodeelectrically connected to the back surface field layer were formed, anda solar cell was manufactured. A plurality of solar cells weremanufactured by differentiating a dose and ion-implantation energy ofthe argon under the conditions stated in the following Table 1.

Comparative Example

A plurality of solar cells was manufactured by the same method asExperimental Embodiment 1 except that argon is not ion-implanted.

TABLE 1 relative value of relative value of ion-implantation Number ofsheet resistance energy samples Experimental 4.5 1 6 Embodiment 1Experimental 3.5 1.6 6 Embodiment 2 Experimental 5.5 1.6 6 Embodiment 3Experimental 30 2.8 6 Embodiment 4 Experimental 45 2.8 36 Embodiment 5Experimental 60 2.8 6 Embodiment 6 Experimental 35 4 6 Embodiment 7Experimental 55 4 6 Embodiment 8 Experimental 45 4.6 6 Embodiment 9

Relative value of sheet resistance of a second portion of an emitterwhere argon is ion-implanted in each of Experimental Embodiments andComparative Examples is measured, and the result is shown in FIG. 8. Therelative value of the sheet increases towards the top of the graph shownin FIG. 8.

Referring to FIG. 8, the second portions of emitter layers of the solarcells according to the Experimental Embodiments have high sheetresistances, compared with those according to the Comparative Example.Also, as the dose and the ion-implantation energy of the argon increase,the sheet resistance increases also. That is, in the ExperimentalEmbodiments, the sheet resistance of the second portions increase, andthus, the recombination of the holes and electrons at the secondportions can be effectively reduced or prevented.

Certain embodiments of the invention have been described. However, theinvention is not limited to the specific embodiments described above,and various modifications of the embodiments are possible by thoseskilled in the art to which the invention belongs without leaving thescope defined by the appended claims.

What is claimed is:
 1. A solar cell, comprising: a semiconductorsubstrate; a first dopant layer formed at one surface of thesemiconductor substrate, wherein the first dopant layer includes a firstconductive type dopant; and a first electrode electrically connected tothe first dopant layer, wherein the first dopant layer includes a firstportion disposed adjacent to the first electrode and a second portionthat is other than the first portion of the first dopant layer, whereinthe second portion of the first dopant layer has a resistance largerthan a resistance of the first portion of the first dopant layer,wherein each of the first portion and the second portion of the firstdopant layer has the first conductive type dopant, wherein at least oneof the first portion and the second portion of the first dopant layerincludes a pre-amorphization element, wherein a concentration of thepre-amorphization element in the second portion of the first dopantlayer is higher than a concentration of the pre-amorphization element inthe first portion of the first dopant layer, wherein the semiconductorsubstrate has a base dopant having a second conductive type opposite tothe first conductive type dopant of each of the first and the secondportions of the first dopant layer, and wherein the pre-amorphizationelement has an atomic number that is larger than an atomic number of thefirst conductive type dopant.
 2. The solar cell according to claim 1,wherein the first portion includes the first conductive type dopantwithout the pre-amorphization element, and wherein the second portionincludes the first conductive type dopant and the pre-amorphizationelement.
 3. The solar cell according to claim 1, wherein thepre-amorphization element includes at least one material selected fromthe group consisting of argon, germanium, and fluorine.
 4. The solarcell according to claim 1, wherein the first portion is thicker than thesecond portion.
 5. The solar cell according to claim 1, wherein, in thesecond portion, the concentration of the pre-amorphization element ishigher than a concentration of the first conductive type dopant.
 6. Thesolar cell according to claim 5, wherein, in the second portion, theconcentration of the pre-amorphization element is about 3 to 20 timesthe concentration of the first conductive type dopant.
 7. The solar cellaccording to claim 1, further comprising: a second dopant layer formedat another surface of the semiconductor substrate, the second dopantlayer including a second conductive type dopant; and a second electrodeelectrically connected to the second dopant layer.
 8. The solar cellaccording to claim 7, wherein the second dopant layer includes a thirdportion disposed adjacent to the second electrode and a fourth portionthat is other than the third portion of the second dopant layer, whereinthe fourth portion of the second dopant layer has a resistance that islarger than a resistance of the third portion of the second dopantlayer, and wherein the fourth portion of the second dopant layerincludes an additional pre-amorphization element.
 9. The solar cellaccording to claim 1, wherein each of the first portion and the secondportion of the first dopant layer includes the pre-amorphizationelement.